From 9968afbe4810665c622664baaa6f76e43890607a Mon Sep 17 00:00:00 2001
From: sacha-renault <sacha35340@gmail.com>
Date: Sat, 5 Jul 2025 21:45:57 +0200
Subject: [PATCH] feat: Add with_sweep_range() method for control over knob
 start position and rotation range. Maintains backward compatibility

---
 examples/example_knob.rs |  6 ++++--
 src/lib.rs               | 36 ++++++++++++++++++++++++++++++++++--
 2 files changed, 38 insertions(+), 4 deletions(-)

diff --git a/examples/example_knob.rs b/examples/example_knob.rs
index f438ad2..11a0690 100644
--- a/examples/example_knob.rs
+++ b/examples/example_knob.rs
@@ -117,7 +117,8 @@ impl eframe::App for KnobExample {
                         egui::Color32::from_rgb(100, 255, 100),
                     )
                     .with_size(50.0)
-                    .with_label_format(|v| format!("{:.2}%", v)),
+                    .with_label_format(|v| format!("{:.2}%", v))
+                    .with_sweep_range(1. / 8., 0.75),
                 );
 
                 ui.add(
@@ -128,7 +129,8 @@ impl eframe::App for KnobExample {
                             egui::Color32::from_rgb(50, 50, 220),
                             egui::Color32::from_rgb(100, 100, 255),
                         )
-                        .with_size(50.0),
+                        .with_size(50.0)
+                        .with_sweep_range(0., 2.),
                 );
             });
         });
diff --git a/src/lib.rs b/src/lib.rs
index c1b687b..5828620 100644
--- a/src/lib.rs
+++ b/src/lib.rs
@@ -1,3 +1,5 @@
+use core::f32;
+
 use egui::{Align2, Color32, Rect, Response, Sense, Stroke, Ui, Vec2, Widget};
 
 /// Position of the label relative to the knob
@@ -42,6 +44,8 @@ pub struct Knob<'a> {
     label_offset: f32,
     label_format: Box<dyn Fn(f32) -> String>,
     step: Option<f32>,
+    min_angle: f32,
+    max_angle: f32,
 }
 
 impl<'a> Knob<'a> {
@@ -69,9 +73,37 @@ impl<'a> Knob<'a> {
             label_offset: 1.0,
             label_format: Box::new(|v| format!("{:.2}", v)),
             step: None,
+            min_angle: -std::f32::consts::PI,
+            max_angle: std::f32::consts::PI * 0.5,
         }
     }
 
+    /// Sets the angular sweep range of the knob
+    ///
+    /// This controls where the knob starts and how far it can rotate. By default,
+    /// knobs start at the bottom-left (135°) and sweep 270° clockwise to bottom-right.
+    ///
+    /// # Arguments
+    /// * `start_angle_normalized` - Starting position as fraction of full circle:
+    ///   - `0.0` = bottom (6 o'clock)
+    ///   - `0.25` = left (9 o'clock)
+    ///   - `0.5` = top (12 o'clock)
+    ///   - `0.75` = right (3 o'clock)
+    /// * `range` - How far the knob can sweep as fraction of full circle:
+    ///   - `0.25` = quarter turn (90°)
+    ///   - `0.5` = half turn (180°)
+    ///   - `0.75` = three-quarter turn (270°)
+    ///   - `1.0` = full turn (360°)
+    ///   - Values > 1.0 create multi-turn knobs
+    pub fn with_sweep_range(mut self, start_angle_normalized: f32, range: f32) -> Self {
+        self.min_angle =
+            start_angle_normalized.rem_euclid(1.) * f32::consts::PI * 2. + f32::consts::PI / 2.;
+
+        // A range of 1. represent a full turn
+        self.max_angle = self.min_angle + range.max(0.) * 2. * f32::consts::PI;
+        self
+    }
+
     /// Sets the size of the knob
     pub fn with_size(mut self, size: f32) -> Self {
         self.size = size;
@@ -210,8 +242,8 @@ impl Widget for Knob<'_> {
 
         let center = knob_rect.center();
         let radius = knob_size.x / 2.0;
-        let angle = (*self.value - self.min) / (self.max - self.min) * std::f32::consts::PI * 1.5
-            - std::f32::consts::PI;
+        let angle = self.min_angle
+            + (*self.value - self.min) / (self.max - self.min) * (self.max_angle - self.min_angle);
 
         painter.circle_stroke(
             center,